1. Field of the Invention
The subject invention relates to apparatus for transporting tape including, but not limited to, magnetic recording tape and photographic film, and comprising an improvement for suppressing a predetermined flutter component.
2. Description of the Prior Art
In obtaining low flutter performance from tape transport machines, the limits to flutter reduction are frequently set by resonances within the tape path. In the extreme case, the self-resonance of the tape mass and its elasticity provide a peak of flutter which usually lies outside of the band of servo correction. Typical techniques of attempting to suppress this resonance involve the addition of rollers, pads or other devices which serve to dampen the resonance, either by means of coulomb friction or viscous damping.
In dealing with this type of damping in wideband servos, the damping mechanism itself must not introduce additional low frequency resonances either individually or in conjunction with the tape. This, in turn, implies that the damping mechanism must be of extremely low inertia. In general, the effect of damping devices is not only to reduce the resonant peak, but also to add a generalized flutter component resembling white noise over the entire spectrum. In consequence, very little improvement or no net improvement at all is realized.
A different type of tunable damping for improving tape velocity-fluctuation performance in tape transports is disclosed in U.S. Pat. No. 3,258,183, by Max Weissbach, issued June 28, 1966 and herewith incorporated by reference herein. The technique disclosed in that patent proceeds on the basis of a development of a slight depression or pucker in an elongate tape within a tape transport vacuum column for the purpose of damping small variations in velocity due, primarily, to variations in web tension during a rapid start in tape motion. Basically, that prior-art technique contemplates an adjustable device connected to the vacuum connection of the vacuum column for a small vacuum recess to adjust the magnitude of the vacuum pull. In particular, that reference proposes the provision of a coupling tube in the vacuum connection having a length equal to approximately 1/8 of the wave length of the particular frequency sought to be eliminated from the tape fluctuation during the start cycle. In the equipment according to that reference, a threaded plug renders the tape velocity-fluctuation damper tunable, in order to provide an adjustable device which has the purpose of greatly reducing the shock waves generated along the tape immediately after start of tape motion and of reducing the time required for tape speed stabilization at the start of tape motion.
By being operative in the vacuum coupling of the equipment, the damping device according to the latter reference cannot be fully effective as an energy-absorbing gas column and is also affected by changes in the vacuum intensity. The provision of the depression or pucker according to the teaching of the latter reference also results in a localized lack of a definite tape guiding surface.
Further vacuum buffering equipment is apparent from U.S. Pat. Nos. 3,065,892 and 3,148,816 while U.S. Pat. No. 3,379,353 shows a positive pressure buffer device for magnetic tape transports. Other prior-art tape damping equipment is apparent from U.S. Pat. Nos. 3,231,165, 3,420,424, 3,495,046, 3,680,734, 3,680,756 and 3,813,019, which are herewith incorporated by reference herein.